The invention relates to a process and a device for the production of 1,2-dichloroethane, hereinafter referred to as “EDC”, which primarily serves as an intermediate product in the production of monomer vinyl chloride, hereinafter referred to as “VCM”, which, in turn, is used to produce polyvinyl chloride (PVC). Hydrogen chloride HCl is obtained when EDC is reacted to produce VCM. Hence, the preferred method of producing EDC from ethylene C2H4 and chlorine Cl2 is such that a balance is maintained between the hydrogen chloride HCl produced and consumed in the various reactions shown below:Cl2+C2H4→C2H4Cl2 (pure EDC)+218 kJ/Mole  (1)C2H4Cl2 (crackable EDC)→C2H3Cl (VCM)+HCl−71 kJ/Mole  (2)C2H4+2 HCl+½O2→C2H4Cl2 (raw EDC)+H2O+238 kJ/Mole  (3)
The process for the production of VCM with an adequate HCl balance, hereinafter referred to as “balanced VCM process”, comprises the following process steps:                direct chlorination, in which one portion of the required EDC is produced from ethylene C2H4 and chlorine Cl2 in the presence of a homogeneous catalyst and made available as so-called pure EDC;        oxychlorination, in which the remaining portion of the required EDC is produced from ethylene C2H4, hydrogen chloride HCl and oxygen O2 and made available as so-called raw EDC;        fractionating EDC purification, in which the secondary products formed in the oxychlorination and EDC pyrolysis sections are removed from the raw EDC, the recycle EDC returned from the VCM fractionation section and, as an option, from the pure EDC in order to obtain a so-called feed EDC suitable for use in the EDC pyrolysis section; if desired, it is also possible to distil the pure EDC from the direct chlorination section in the heavy ends column of the EDC distillation section;        EDC pyrolysis, in which the feed EDC is thermally cracked; the mixture leaving the reactor is the cracked gas which consists of VCM, hydrogen chloride HCl and non-reacted EDC as well as secondary products;        VCM fractionation, in which the desired pure VCM product is separated from the cracked gas, while the other essential substances, viz. hydrogen chloride HCl and non-reacted EDC, contained in the cracked gas are recovered separately in the balanced VCM process and returned as recycle HCl or recycle EDC.        
In most industrial-scale processes, a circulating stream of EDC reaction product is used as the reaction fluid in the direct chlorination section. The circulating stream can be generated in a loop-type reactor with external or internal circulation system. The circulating stream can also be generated in a system with forced or natural circulation. In most cases, ferric chloride is used as catalyst; in addition, sodium chloride, which can inhibit the formation of heavy ends, may be admixed as an additive.
The state of the art as regards direct chlorination is, for instance, described in DE 199 10 964 A1. The process according to DE 199 10 964 A1 aims at suppressing side reactions, especially the continuation of the chlorination process of EDC to 1,1,2-trichlorethane, by letting most of the chlorination reaction to take place in the homogeneous liquid phase. The ethylene, which is less readily soluble in EDC than chlorine, is completely dissolved in the main stream of the circulating EDC reaction fluid in a co-current bubble column. The chlorine, which is more readily soluble in EDC than ethylene, is dissolved in a super-cooled EDC part-stream and the resulting solution of chlorine in EDC is fed to the circulating main stream which already contains the dissolved ethylene.
Reaction (1) is usually run with a slight surplus of ethylene, in order to rule out corrosion problems in the reaction system, intensified formation of secondary products and problems involved in the treatment of chlorine-bearing waste gas streams. The reactor is supplied with a ratio-controlled feed of chlorine and ethylene, the ethylene content of the stream leaving the reactor serving as the control variable. The general aim for economical reasons is to minimise the surplus of ethylene at the reactor outlet in order to avoid excessive losses of ethylene.
It was further found that the formation of secondary products in reaction (1) was particularly low when running the reaction completely in the liquid phase, as also described in WO 03/070673 A1. To achieve this, it is required to make the ethylene dissolve completely in the reaction tube before the dissolved chlorine is added. The small gas bubbles initially produced by the gas feed device will grow along this section by coalescence and will finally reach a constant equilibrium variable resulting from coalescence and disintegration processes. This is an effect with a negative impact on the exchange of materials as the surface available for the exchange of fluids involved will become smaller as the bubble diameter becomes larger with a certain total volume of gas.
Reaction (1) in the subsequent reaction section, which is homogenous for the most part, proceeds kinetically according to a second-order velocity law. If both reactants initially have a stoichiometric ratio or if one reactant is in slight surplus, the reaction will proceed more slowly than it would if one reactant such as ethylene, for example, were initially present in a higher surplus in reaction (1). Transferred to a reactor of the type described herein, this means that the reaction is completed after a shorter run in the circulating reaction fluid stream than this would be the case with a lower initial surplus in ethylene.
The combination of the effects in ethylene dissolution, the reaction itself and at the commencement of boiling determines the dimensions of the reactor according to the conventional state of the art and makes it difficult to increase the capacity at a later stage.
The aim of the present invention, therefore, is to provide an economical process as well as a device which will permit an increase of the capacity without enlarging the external reactor dimensions while producing EDC of high purity.